1. Field of Invention:
This invention relates generally to anchors for securing fixtures or other parts to masonry surfaces, and more particularly to a one-piece, pre-shaped anchor which when forcibly driven into a hole drilled into the masonry becomes securely lodged therein.
2. Prior Art:
It is frequently necessary to secure fixtures or other parts against the surface of masonry. The term "masonry" as used herein encompasses not only brickwork and concrete but all rigid non-metallic structural materials such as stone and plaster. The conventional practice for this purpose is to make use of an anchor bolt assembly which includes an expansible shell that is caused to expand when the bolt is turned by a wrench or other torque-producing tool, the expanded shell gripping the wall of the hole to securely retain the bolt therein.
Typical of such anchor bolt assemblies is the type disclosed in the Giannuzzi patent No. 3,766,819 in which a cone at the rear of the bolt is caused to advance toward an expansible shell encircling the bolt when the bolt is rotated, the expanded shell acting to anchor the bolt in the hole. Anchor bolt assemblies operating in a similar manner are disclosed in the patent No. to McIntyre, 4,056,037 and the Dempsey patent No. 2,988,950.
Quite apart from the fact that conventional anchor bolt assemblies are composed of two or more cooperating components and are relatively expensive to manufacture, are the difficulties often experienced in making installations with such assemblies.
On a major construction site, it is generally necessary to use literally hundreds or thousands of anchor bolts to secure such items as suspended ceilings, soffits and wall studding, or to make similar attachments requiring repetitive anchor bolt operation. In each of these, the bolt must be installed in a carefully drilled hole. The bolt must be properly inserted in the hole and then turned by a tool until the bolt is locked in the hole by its associated expansible shell. This requires a significant degree of care by the installer. A large number of anchor failures arise from unqualified installers who fail to drill an accurate hole or to adequately torque the anchor. Moreover, there is no way of knowing whether the anchor is not holding properly until it fails in service, and this may have tragic consequences.
Apart from the problem of improper installation, is the fact that with existing anchor bolts, the installation of each bolt is a time-consuming operation. Since at a given site, this operation must be repeated over and over again, the operator in the course of a working day is only able to install a limited number of anchor bolts. This adds substantially to construction site labor costs.
In order to reduce the time involved in installing anchor bolts, anchors have been proposed which are driven into pre-drilled masonry holes, thereby obviating the need to turn in the anchor bolt to expand a wedging shell. Thus the patent No. to Nillson, 3,894,469 discloses a nail-like anchor which when hammered into a hole has a weakened portion that is deformed by this action to effect the desire wedging. The Gutshall patent No. 3,518,915 also shows a one-piece expandable anchor. Other patents, such as Patruch No. 3,022,701, show two-piece driven anchors in which a nail-like element is hammered into an expansion sleeve. In these prior arrangements, the anchor bolt assembly still depends on an expansion element or equivalent means that is formed outwardly against the wall of the hole by the hammering action.
Also of prior art interest is the single piece anchor marketed under the trademark "Rawl Drive" by the Rawlplug Company, Inc., of New Rochelle, N.Y. This anchor has a resilient shank, an intermediate section of which is split into two half sections having a semi-circular cross-section. These are expanded in opposite directions in the plane of the split. The unsplit diameter of the shank is significantly smaller than the diameter of the masonry hole in which the anchor is to be installed, whereas the maximum diameter of the split section is somewhat greater than that of the hole.
In making a "Rawl Drive" anchor, one starts with an annealed piece of steel which is first cold headed into a simple rivet-like shape. In order to then split the intermediate section of the shank into two half sections and to expand these half sections in opposite directions in the plane of the split to create the desire bulge, one must heat treat the anchor to impart thereto sufficient hardness to react to the splitting tool; for otherwise, the then ductile metal will yield and will not split. After completion of the splitting and expansion operation, the anchor must again be heat treated to a spring-like temper to render the expanded split section resilient and compressible. Because of this relatively complex procedure, the "Rawl Drive" anchor is quite expensive to make.
When the "Rawl Drive" anchor is driven into a hole drilled in masonry, the expanded half sections thereof are compressed inwardly and straightened out. But because of the resilience of the half-sections, they seek to resume their normal expanded shape, thereby imposing an anchoring force on the wall of the masonry hole on opposite sides thereof. The remainder of the shank imposes no anchoring force on the drilled hole; hence whether the anchor is long or short, there is no substantial difference in the anchoring force.
Being axially split and expanded, the half sections of the shank only make contact with the surface of the hole in a region adjacent to the plane of the split. This provides mating contact of approximately 45 degrees on each split half, and the resultant holding power is low.
A serious drawback of the "Rawl Drive" anchor is that the bulge created by the split and expanded half sections has a maximum transverse dimension which is necessarily significantly greater than the diameter of the hole drilled in the masonry, and consequently is greater than the diameter of the mounting hole in the fixture to be attached to the masonry wall by the anchor bolt. Because a "Rawl Drive" anchor, before entering the masonry hole, must first pass through the mounting hole in the metal fixture, the use of conventional fixtures in conjunction with "Rawl Drive" anchors is precluded. That is to say, one cannot use the "Rawl Drive" anchor with a fixture whose mounting hole has a diameter which corresponds to that of the drilled hole, which is usually the case, for the Rawl Drive anchor cannot go through this mounting hole.